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Advantages of suppositories
• Suitable for drugs destroyed by pH or enzymatic activity of the GIT.
• Suitable for drugs irritating to stomach
• Suitable for drugs that suffer from first-pass effect (bypass the portal circulation).
• Suitable for patients unable to swallow.
• Suitable for patients suffering from vomiting.

Disadvantages of suppositories
• Uncomfortable.
• Variation of absorption pattern, unpredicted bioavailability.
• Irritation for mucus by some drugs or bases.
• Slow and erratic absorption or loss of suppository due to defecation.
• Pathology (hemorrhoids, fissures) may lead to irritation and expulsion.

Physiological factors influence the drug absorption from rectal suppositories.
• The human rectum is approximately 15 to 20 cm long. When empty of fecal material, the
rectum contains only 2 to 3 mL of inert mucous fluid.
• In the resting state, the rectum is not motile; there are no villi or microvilli on the rectal
mucosa.
• However, there is abundant vascularization of the submucosal region of the rectum wall
with blood and lymphatic vessels.

Effect of colonic contents
• When systemic effects are desired, greater absorption may be expected from a rectum that
is void than from one that is distended with fecal matter.
• A drug will have a greater opportunity to be in contact with the absorbing surface of the
rectum and colon in an empty rectum. Therefore, an evacuant enema may be administered
and allowed to act before the administration of a suppository.
Other conditions, such as diarrhea, colonic obstruction due
to tumorous growths, and tissue dehydration can all influence the rate and degree of drug
absorption from the rectum.

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